Frequency doublers are implemented in a variety of applications where design or physical limitations of a device prevent internal generation of a desired frequency. In such an application, a frequency doubler creates the desired frequency by multiplying two signals together. Typically, two sine wave signals that are 90 degrees out of phase and have the same frequency are multiplied, resulting in a signal having a frequency equal to twice the frequency of the two sine waves.
In many applications, the multiplication of the two sine wave signals in the frequency doubler is accomplished using a single Gilbert cell mixer. In these applications, timing differences between the paths associated with the two signals result in phase errors between the two signals, thereby causing the emergence of even order harmonics of the frequency doubled signal.
Some applications require the generation of quadrature signals from the frequency doubled signal. In these applications, the frequency doubled signal is typically passed through a phase shifter in order to create the quadrature signals having the desired frequency. However, the phase shifter has an associated loss, thereby reducing the signal power and ultimately the signal-to-noise ratio of the quadrature signals at the output of the frequency doubler network. Thus, there remains a need for a quadrature frequency doubler which eliminates the need for the phase shifting of the frequency doubled signal. Further, there remains a need for a quadrature frequency doubler capable of minimizing second order differential and common mode distortion and suppressing even order harmonics of the frequency doubled signal.